Degradation Of Ionic Liquids In Ultrasound And Nanoscale Zerovalent Iron/Hydrogen Peroxide System

Ionic liquids （ILs） are considered to be the21st century environment-friendly greensolvent because of its inherently unique physical and chemical properties, such as wideliquid range, low vapor pressure, good thermal stability. However, with the extensiveapplication and in-depth study, people gradually discovered that the majority of ionicliquids are commonly toxic and difficult to biodegradation and thermal decompositionin nature. Currently, the study of ILs has mainly focused on their physical-chemicalproperties and application; there is limited attention on wastewater treatment andenvironmental impact assessment of ILs.In this paper, the degradation of some ionic liquids by the ultrasound assistednanoscale zerovalent iron with hydrogen peroxide system （US-nZVI/H₂O₂） werestudied. The main contents include the following components:（1） The optimal experimental conditions and reaction kinetics on oxidative degradation of1-butyl-3-methylimidazolium bromide （[C₄mim]Br） ionic liquid by the ultrasound and nanoscalezerovalent iron/hydrogen peroxide system were studied. The results showed that [C₄mim]Br ionicliquid was effectively degraded in the ultrasound and nanoscale zerovalent iron/hydrogenperoxide system. The degradation efficiency of [C₄mim]Br could reach90.8%under thefollowing conditions: nZVI0.25g·L^-1, H₂O₂60mmol·L^-1, reaction system initial pH was3andreaction time120min at30℃. It is found that the oxidative degradation of [C₄mim]Br was mainlyascribed to OH oxidation and could be described by the second order kinetics model with respectto the concentration of [C₄mim]Br.（2） The degradation efficiency of other ionic liquids by the ultrasound and nanoscalezerovalent iron/hydrogen peroxide system was studied. It is found that ionic liquidswith different head group types, such as imidazolium, morpholinium, pyrrolidinium,pyridinium and piperidinium ionic liquid can also be significantly degraded. Thedegradation process follows the second order reaction kinetics model. Addition, the composition of imidazolium-based ionic liquids has a significant effect on theirdegradability. The degradation efficiency decreased gradually with the increase of thealkyl sidechain length of1-alkyl-3-methylimidazolium ionic liquid, but the type ofanion of imidazolium ionic liquid is no obvious influence on its degradation.（3） The detection results has been showed about total organic carbon （TOC） anddegradation rate of ionic liquids by the ultrasound and nanoscale zerovalent iron/hydrogenperoxide system. The results demonstrated that studied ionic liquids have higherdegradation efficiency by degradation of120min and meanwhile, the mineralizationrate was very low. That is because other organic compounds may be generated in thedegradation process of ionic liquids.